AN UNCONFINED COMPRESSION TESTING MACHINE
FOR MARINE SEDIMENTS

by

Richard Karl Westfahl

United States
Nava! Postgraduate Schoo

rm t

AN UNCONFINED COMPRESSION TESTING MACHINE

FOR
MARINE SEDIMENTS

by

Richard Karl Westfahl

September 1970

TkU document hat been appnjovtd ^ofi public, fit-
Iza&e. and 6alz; aM> cLuVUbutcon <Lt> untirxitzd.

T136842

An Unconfined Compression Testing Machine
for Marine Sediments

by

Richard Karl^Westfahl
Lieutenant Commander, United States Navy
B.S., United States Naval Academy, 1959

Submitted in partial fulfillment of the
requirements for the degree of

MASTER OF SCIENCE IN OCEANOGRAPHY

from the

NAVAL POSTGRADUATE SCHOOL
September 1970

RARY

AL POSTGRADUATE SCHOOE

TEREY, CALIF. 93940 .

ABSTRACT

The two most common laboratory test methods used for measuring the
undisturbed or original shear strength of marine sediments are the vane
shear test and the unconfined compression test. The application of the
load in the unconfined compression test is accomplished either in a strain-
controlled or a stress-controlled manner. An unconfined compression testing
machine was constructed to allow application of the load by either the
strain-controlled or stress-controlled method, and it was specifically
designed to accurately test marine sediments having relatively low values
of shear strength. A unique feature of the apparatus is that it provides
a continuous plot of displacement versus load throughout the test procedure.
Tests for shear strength in the two load application modes were conducted
on gravity cores taken on the continental slope between San Francisco and
Monterey. Results of the tests compared favorable with each other, as
well as with values secured from vane shear testing. The tests suggest
that these particular sediments have friction angles approximating 30
degrees.

TABLE OF CONTENTS

I. INTRODUCTION 15

GENERAL 15

MARINE SEDLMENT STRUCTURE 15

SHEAR STRENGTH THEORY 17

UNCONFINED COMPRESSION TEST 18

General 18

Apparatus 20

Controlled Strain Procedure 21

Controlled Stress Procedure ... 21

Calculations "...22

II. DESIGN CONSIDERATIONS 23

GENERAL 23

FORCE TRANSDUCER 23

DISPLACEMENT TRANSDUCER ...... 24

VARIABLE SPEED MOTOR, CONTROLLER AND JACTUATOR . . 24

RECORDING OF LOAD AND DISPLACEMENT ........ 25

POWER SUPPLY 25

STRUCTURAL COMPONENTS 26

BALL BUSHING 26

III. NPS UNCONFINED COMPRESSION TESTING MACHINE 27

GENERAL DESCRIPTION 27

FORCE TRANSDUCER 31

DISPLACEMENT TRANSDUCER 34

TRANSDUCER AMPLIFIER- INDICATOR 35

MACHINE SCREW JACTUATOR 38

VARIABLE SPEED MOTOR 39

MOTOR SPEED CONTROLLER 39

X-Y RECORDER . 41

STRUCTURAL COMPONENTS 41

DISPLACEMENT TRANSDUCER SUPPORT BRACKET 42

JACTUATOR SHAFT UPPER PLATEN 47

JACTUATOR SPACER 47

SHAFT EXTENSION ARMS 47

WEIGHTED PISTON ASSEMBLY 51

LEAD DISCS 51

BALL BUSHING AND PILLOW BLOCK i . . 53

IV. TEST PROCEDURES 54

GENERAL 54

INITIAL ADJUSTMENT OF THE TRANSDUCER AMPLIFIER-
INDICATORS 54

CALIBRATION OF THE TRANSDUCER AMPLIFIER-
INDICATORS o 56

MACHINE CONVERSION TO THE STRAIN-CONTROLLED

MODE 58

MACHINE CONVERSION TO THE STRESS -CONTROLLED

MODE 59

PREPARATION OF THE UNDISTURBED SAMPLE . 60

TESTING IN THE STRAIN -CONTROLLED MODE 62

TESTING IN THE STRESS -CONTROLLED MODE 63

V. TEST RESULTS 65

VI. CONCLUSIONS 138

VII. RECOMMENDATIONS FOR FURTHER RESEARCH 139

BIBLIOGRAPHY . 140

INITIAL DISTRIBUTION LIST 142

DD FORM 1473 143

'

(

LIST OF TABLES

I. Core Data Summary 67

II. Core Data Summary Sheet, Core No. 1W 68

III. Core Data Summary Sheet, Core No. 2W 69

IV. Core Data Summary Sheet, Core No. 3W 70

V. Core Data Summary Sheet, Core No. 4W 71

VI. Core Data Summary Sheet, Core No. 5W 72

VII. Core Data Summary Sheet, Core No. 6W 73

VIII. Core Data Summary Sheet, Core No. 7W 74

IX. Core Data Summary Sheet, Core No. 8W 75

X. Core Data Summary Sheet, Core No. 9W , ... 76

XI. Core Data Summary Sheet, Core No. 10W 77

XII. Core Shear Strength Comparison Table,

Core Numbers 1W through 5W 122

XIII. Core Shear Strength Comparison Table,

Core Numbers 6W through 10W 123

XIV. Core Failure Plane Summary Table 125

■-■

)

0

i

LIST OF FIGURES

Figure

1. Mohr Circle Diagram of the Unconfined Compression

Test 19

2. The NPS Unconfined Compression Testing Machine

in the Strain-Controlled Mode 28

3. The NPS Unconfined Compression Testing Machine

in the Stress-Controlled Mode 29

4. The Model 300D Amplifier-Indicators and the X-Y
Recorder 30

5. The Force Transducer and the Displacement

Transducer 32

6. Detail of the Base and the Support Columns 43

7. Detail of the Lower Platform : . . . 44

8. Detail of the Upper Platform 45

9. Detail of the Displacement Transducer Support

Bracket 46

10. Detail of the Jactuator Shaft Upper Platen 48

11. Detail of the Jactuator Spacer 49

12. Detail of the Shaft Extension Arms 50

13. Detail of the Weighted Piston Assembly 52

14. The Coping Saw, Soldering Gun and Guide Collar 61

15. Core Locations 66

16. Strain-Controlled Load versus Sample Height Curves

for Core 1W 79

17. Stress-Controlled Load versus Sample Height Curves

for Core 1W 80

18. Strain-Controlled Load versus Sample Height Curves

for Core 2W 81

19. Stress-Controlled Load versus Sample Height Curves

for Core 2W .82

Figure

20. Strain-Controlled Load versus Sample Height Curves

for Core 3W 83

21. Stress-Controlled Load versus Sample Height Curves

for Core 3W 84

22. Strain-Controlled Load versus Sample Height Curves

for Core 4W 85

23. Stress-Controlled Load versus Sample Height Curves

for Core 4W 86

24. Strain-Controlled Load versus Sample Height Curves

for Core 5W 87

25. Stress-Controlled Load versus Sample Height Curves

for Core 5W 88

26. Strain-Controlled Load versus Sample Height Curves

for Core 6W 89

27. Stress-Controlled Load versus Sample Height Curves

for Core 6W 90

28. Strain-Controlled Load versus Sample Height Curves

for Core 7W 91

29. Stress-Controlled Load versus Sample Height Curves

for Core 7W 92

30. Strain-Controlled Load versus Sample Height Curves

for Core 8W 93

31. Stress-Controlled Load versus Sample Height Curves

for Core 8W 94

32. Strain-Controlled Load versus Sample Height Curves

for Core 9W 95

33. Stress-Controlled Load versus Sample Height Curves

for Core 9W 96

34. Strain-Controller Load versus Sample Height Curves

for Core 10W 97

35. Stress-Controlled Load versus Sample Height Curves

for Core 10W 98

36. Strain-Controlled Stress versus Strain Curves

for Core 1W 101

10

Figure

37. Stress-Controlled Stress versus Strain Curves

for Core 1W 102

38. Strain-Controlled Stress versus Strain Curves

for Core 2W 103

39. Stress-Controlled Stress versus Strain Curves

for Core 2W 104

40. Strain-Controlled Stress versus Strain Curves

for Core 3W 105

41. Stress-Controlled Stress versus Strain Curves

for Core 3W 106

42. Strain-Controlled Stress versus Strain Curves

for Core 4W 107

43. Stress-Controlled Stress versus Strain Curves

for Core 4W 108

44. Strain-Controlled Stress versus Strain Curves

for Core 5W 109

45. Stress-Controlled Stress versus Strain Curves

for Core 5W 110

46. Strain-Controlled Stress versus Strain Curves

for Core 6W Ill

47. Stress-Controlled Stress versus Strain Curves

for Core 6W 112

48. Strain-Controlled Stress versus Strain Curves

for Core 7W 113

49. Stress-Controlled Stress versus Strain Curves

for Core 7W 114

50. Strain-Controlled Stress versus Strain Curves

for Core 8W 115

51. Stress-Controlled Stress versus Strain Curves

for Core 8W 116

52. Strain-Controlled Stress versus Strain Curves

for Core 9W 117

53. Stress-Controlled Stress versus Strain Curves

for Core 9W 118

11

Figure

54. Strain-Controlled Stress versus Strain Curves

for Core 10W 119

55. Stress-Controlled Stress versus Strain Curves

for Core 10W 120

56. Shear Strength versus Depth Curves

for Core 1W 126

57. Shear Strength versus Depth Curves

for Core 2W 127

58. Shear Strength versus Depth Curves

for Core 3W 128

59. Shear Strength versus Depth Curves

for Core 4W 129

60. Shear Strength versus Depth Curves

for Core 5W 130

61. Shear Strength versus Depth Curves

for Core 6w 131

62. Shear Strength versus Depth Curves

for Core 7W 132

63. Shear Strength versus Depth Curves

for Core 8W 133

64. Shear Strength versus Depth Curves

for Core 9W 134

65. Shear Strength versus Depth Curves

for Core 10W 135

66. Typical Failed Samples 136

12

ACKNOWLEDGEMENTS

The author wishes to thank Dr. Raymond J. Smith, Professor of Oceano-
graphy, Naval Postgraduate School, for his advice and encouragement in
the development of this machine. Appreciation is also expressed to the
Machine Facility, the Photographic Department, and to Miss Georgia
Galloway for secretarial assistance. The author is also grateful for the
interest and support provided by the Naval Facilities Engineering Com-
mand. Finally, the author is indebted to his wife Dianne for her continued
patience and understanding during the period of postgraduate studies.

13

I. INTRODUCTION

GENERAL

An effort has been made in recent years to determine more about the
mass physical properties of the sediments present on the ocean floor.
Both private industry and governmental agencies have contributed greatly
to these programs. It is necessary that much more be accomplished along
these lines, particularly as to the quantity and quality of the data obtained
from areas deeper than the continental shelf.

One of the chief physical properties of marine sediments that is often
measured is its shear strength. The two most commonly used tests to deter-
mine this are the vane shear and the unconfined compression tests. A vane
shear apparatus was built by Minugh (1970) and modified by Heck (in press)
to specifically measure the vane shear strength of these soft marine sedi-
ments. An unconfined compression testing machine has also been designed and
constructed to accurately measure sediment shear strength by use of either
the strain-controlled or stress-controlled mode of loading, and it is
described herein. A brief summary of marine sediment structure, shear
strength theory and the unconfined compression test are presented in the
following sections.

MARINE SEDIMENT STRUCTURE

Most of the marine sediments found on the ocean floor in water greater
than continental shelf depth consist primarily of either (Keller, 1968):

1. Extremely fine-grained inorganic pelagic clays.

2. Calcareous ooze consisting of at least 30 percent calcium
carbonate tests. * ^

15

3. Siliceous ooze consisting of at least 30 percent siliceous
material formed from diatom and radiolarian debris.

The marine clays vary considerable in coloration. In that they are
primarily composed of minerals which tend toward basal cleavage, the clay
particles are either terraced platelets or rod-shaped in appearance. Such
shapes offer a large amount of surface area which is important in consider-
ing the nature of sediment strength. Both calcareous and siliceous plank-
tonic skeletons similarly have relatively large surface areas and general-
ly have disc or elongated shapes.

The fine-grained soil particles tend to flocculate or form loose-knit
aggregations in settling to the sea floor. Rod-shaped or elongated parti-
cles are visualized as forming a random "match-stick" structure, causing
the sediment to have high values of shear strength due to an interlocking
of particles in all directions. Flocculated platelet-shaped particles
characterized by edge-to-face contact between adjacent particles initially
retain their flocculent structure unless disturbed. This is the result of
a large osmotic pressure being created between the platelet faces. This
osmotic pressure apparently results from the attraction of negative ions
to these faces, which in turn repel each other and keep face-to-face con-
tacts to a minimum. There is some evidence that a slight positive charge
exists on the platelet edges. Such a structure is very weak and unstable,
and any disturbance such as a shearing force or sediment compression causes
the angle between the platelets to be reduced. Since the repulsive force
varies inversely with platelet spacing, the platelets become parallel and
separated from each other resulting in a more stable and stronger structure
characterized by the solid platelets being dispersed in a continuous liq-
uid matrix (Hough, 1969).

16

SHEAR STRENGTH THEORY

The shearing strength of a material is its ability to withstand
shearing stresses. When a maximum resistance is exceeded, slippage oc-
curs resulting in failure. In most natural materials the shearing
strength is made up of both an internal friction, a resistance due to
physical contact between the particles, and a cohesion. The cohesion
represents the strength not due to friction, and its exact nature and
source is not well known.

The concept of shear strength has its beginning with the classical
Coulomb equation:

s = c + p tan $
where

s = Shearing strength.

c = Cohesion.

p = Normal stress .

0 = Angle of internal friction.

In soils, Terzaghi's statement of the principle of effective stress
in which the pore water pressure is subtracted from the normal stress to
give an effective normal stress modifies the Coulomb equation to:

s = c + (p-u) tan 0 or

s = c + p' tan 0
where

u = Pore water pressure .
p' = Effective normal stress.
Solid friction is generally considered to be negligible between particles
in saturated marine sediments when they are stressed in an undrained
manner with no loss of pore water (Keller, 1968), and therefore the angle

17

of internal friction is taken to be equal to zero. In such a case, the
shear strength of the sediment is equal to its cohesion.

A simple and rapid laboratory test to measure the shear strength of
a cohesive sediment is the unconfined compression test. The simplicity
of the test makes it one of the most widely used tests conducted on co-
hesive sediments. Furthermore, though it requires removal of the sedi-
ment sample from its core liner prior to testing, this mode of testing
provides excellent shear strength data for experimental and comparison
purposes.

UNCONFINED COMPRESSION TEST

General

The unconfined compression test measures the compressive strength of
a cylindrical sediment sample. It does not require any lateral support due
to its cohesion. On the Mohr circle diagram shown in Figure 1, shear
strength AB is equal to BC cos 0, or

^ or

[j = BC cos 0 = -—- cos 0

For a friction angle of 30 degrees, the shear strength would be approxi-
mately 0. 433£f^, where <JJ" is the major principal stress. Precise measure-
ments have established that a lower value of strength is inherently obtained
in the unconfined compression test compared to results from other test techni-
ques. This may result from the fact that no lateral support is given to the
sample during testing. Shear strength is generally taken to be one-half the
major principal stress (Lambe, 1951). This corresponds to the assumption that
for marine sediments the angle of internal friction is zero.

The unconfined compression test is usually conducted at the natural
water content of the "in-situ" sample, and efforts are made to minimize the

18

Mohr Circle Diagram

of the
Unconfirmed Compression

Test

Figure 1.

19

time the sample is exposed to normal humidities to prevent surface drying.
Although slight drainage occurs on the exposed sides of the sample, the
effect is negligible and the test is considered to be undrained.

The two major advantages of this test over the direct shear test are
that more uniform stresses and strains are imposed and that the failure
plane occurs at the weakest portion of the sample and is not forced to
occur along a predetermined surface.

This test has two advantages over use of the triaxial test when dealing
with marine sediments. It is quick and simple and offers less opportunity
for sample disturbance during testing preparations. This is particularly
the case when handling marine sediments having low values of shear strength.
If the sediment strength is too low, the samples lack sufficient coherence
to permit their being tested in the unconfined mode and either the triaxial
or preferably the vane shear test must be made. The following sections
describe recommended apparatus, procedures, and calculations to be used
when conducting unconfined compression tests (ASTM, 1964).

Apparatus

Compressing the sample may be accomplished with a hydraulic loading
device, an air loading apparatus, a deadweight load system or any other
compressive technique with sufficient capacity and control to provide a
rate of loading of one-half to two percent per minute of controlled axial
strain or application of 1/10 to 1/15 of the estimated failure load every
30 seconds using the controlled stress procedure. For unconfined compres-
sive stresses in the range less than 13.9 pounds per square foot, the device
should be capable of measuring the unit load to at least 0.139 pounds per
square foot.

20

The displacement indicator should measure to an accuracy of 0.001
inches, with a range of travel at least 20 percent of the sample height.
A vernier caliper should also be available to assist in measuring the
physical dimensions of the sample to the nearest 0.01 inches.

The moisture content of the sample should be measured with a drying
oven with thermostatic controls at a temperature at 110 plus or minus five
degrees Centigrade. A balance accurate to 0.01 grams should be available.

A timing device accurate to the nearest second is needed to determine
both the rate of strain and the time increments for load application.

Controlled Strain Procedure

In making a controlled strain test, the sample is placed on the loading
device in the center of the bottom platen and the upper pla„ten is carefully
positioned so that it just makes contact with the sample. The displacement
indicator is then recorded or zeroed. The load application is adjusted to
produce an axial strain rate of one-half to two percent per minute. Load
and displacement values are recorded at least every 30 seconds. The rate
of strain should be regulated so that sample failure occurs within a ten
minute period. For the weaker marine sediments the greater rate of strain
may be used. Loading is continued until either the load decreases with in-
creasing strain or a 20 percent strain is reached. The moisture content of
the sample is determined and a sketch of the sample made showing the angle
of the failure plane.

Controlled Stress Procedure

In the controlled stress procedure an estimate is made of the load
required to cause failure. The sample is then placed on the center of the
loading device bottom platen. The upper platen is carefully positioned so
that it just contacts the sample and the displacement indicator is then

21

recorded or zeroed. An initial load equal to 1/10 to 1/15 the estimated
failure load is placed on the sample. After 30 seconds the displacement
indicator is read and a second load equal to the first is added. Load
increments are added at 30 second intervals and sample displacement is
recorded prior to each load application. The procedure is continued until
either the sample fails or the 20 percent strain limit is reached. The
moisture content of the sample is measured and a sketch of the sample is
made.

Calculations

The axial strain, £ , is computed as follows:

t. H
where

AH = Change in sample height for a given load.

H = Initial sample height.

Using this value for axial strain the average cross-sectional area, A, for

a given load is determined from:

A
A = °

1-6

where

A = Initial sample cross-sectional area
o

The unit shear strength is calculated from:

P

2A

T = —

where

P = Given applied load.

A = Corresponding cross-sectional area.

A plot is made of unit shear strength versus the corresponding axial strain.

The maximum unit shear strength on this curve, or the unit shear strength at

20 percent strain, whichever occurs first, is considered as the shear strength

value.

22

II. DESIGN CONSIDERATIONS

GENERAL

Numerous unique problems are encountered in the design of an unconfined
compression testing machine for use specifically for low strength marine
sediments. A method must be devised to measure the load applied to the
sample in the range of values expected to cause shearing. The displacement
must be precisely measured during compression. The device should be cap-
able of conducting both strain-controlled and stress-controlled tests if it
is to be useful for research- type efforts in the laboratory. The machine
should also have the capability of varying such test parameters as the strain
rate, load increments, and range of displacement. The following sections out-
line some of the factors which were considered in the selection of the major
components of the Naval Postgraduate School (NPS) unconfined compression
testing machine as constructed.

FORCE TRANSDUCER

One of the most important components of the apparatus is the device
which measures the applied load. Most such test machines are equipped with
either a proving ring, a hydraulic oil pressure gage, an air pressure gage,
or a scale which measures the compressive load being placed on the sample.
Some stress-controlled devices simply use the value of the known weight in-
crement and assume that this entire weight is transmitted to the sample
(Richards, 1961). To accurately determine the values of load applied
directly to the sample in the extremely low range of 0 to 50 pounds, a
force transducer was considered the most satisfactory and economical device.
The transducer chosen has a weighing platform on which the sample is
placed during the test, and this allows consideration of the effects that

23

the sample weight might have in the shear strength determination. Losses
occurring due to friction, torque variations, and vibrations are accounted
for, since any directly applied static or dynamic force is precisely mea-
sured.

A transducer produces an electrical output signal which is amplified
and sent to an X-Y recorder. This provides a permanent load record and
eliminates the necessity for reading and recording load values during the
test.

DISPLACEMENT TRANSDUCER

The second major measuring device used on the unconfined compression
testing machine as designed is the displacement transducer. A dial indi-
cator is used on most machines to detect sample displacement, and this
requires the operator to regularly read and record the displacement value.
This evolution is usually combined with the reading of a timer and the
simultaneous reading and recording of the load value. Time lags occur be-
tween these steps and operator errors are introduced because the dials are
being read and the values are being recorded. These time lags and operator
errors are eliminated by use of a displacement transducer, as it produces a
continuous electrical output signal of the precise value of the displace-
ment. The plot of this signal provides a permanent record which can be
used to extract values of displacement at any sample height. A complete
record of what occurs throughout the test is considered superior to a point-
to-point faired curve, and this represents the prime reason that a dis-
placement transducer was selected to measure sample displacement

VARIABLE SPEED MOTOR, CONTROLLER AND JACTUATOR

It is desirable to have a load transmission device which encompasses

24

the range of load expected during testing and allows the rate of load
application to be varied. An off-the-shelf reduction gear, which reduces
the driving force speed to the extremely slow strain rates required by the
unconfined compression test, should be obtained. This eliminates the need
to manufacture these components locally. Every attempt should be made to
use precision gears so as to eliminate vibrations being transmitted from
the driving force to the sample. Allowance for variation of the strain
rates must also be considered. Hand cranks and constant speed motors do not
allow changes in output shaft speed unless gearing is changed. This usually
leads to additional costs and alignment problems. A variable speed DC motor
with its own control circuitry is ideal for rotating at constant speed over
the full range of rated torque. These types of motors and controls can be
readily obtained in the speed and torque ranges necessary for the testing
of marine sediments.

RECORDING OF LOAD AND DISPLACEMENT

The obtaining of a permanent record in the form of a continuous graph
of load versus sample displacement represented the main design goal of
this unconfined compression testing machine. This eliminates the need for
an operator to periodically read and record values of load and displace-
ment, and further permits examination of the entire test profile. Vibra-
tions, variations in torque transmission, frictional losses, and the shear
microstructure of the sample can be detected. Equipment malfunctions,
observable as deviations from normally expected recordings, can be corrected
prior to test continuation.

POWER SUPPLY

Electrical and electronic components of the unconfined compression

25

testing machine should be self-contained in the regulating, rectifying and
transforming of their own power supplies. Each component must be capable
of being powered from the normally available 115 volt, 60 Hertz, grounded
supply. Overload and short-circuit protection should be integral parts of
these components.

STRUCTURAL COMPONENTS

A lightweight, sturdy machine fabricated from relatively inexpensive
corrosion resistant materials is a major design consideration. Availabil-
ity of both materials and machining facilities must also be considered. Al-
though not meant to be portable, the unconfined compression testing machine
should be light enough in weight to facilitate movement around the laboratory.
A sturdy platform should be provided for the machine components to elimin-
ate any transmission of vibrations from either surrounding equipment or the
motor of the machine itself.

BALL BUSHING

The loss due to friction of load transmission in the stress-controlled
mode of testing should be kept to a minimum. This insures that the pre-
selected weight increment is fully transmitted to the sediment sample. A
friction-free bushing should be considered when selecting the guiding de-
vice for the shaft.

26

III. NPS UNCONFINED COMPRESSION TESTING MACHINE

GENERAL DESCRIPTION

The NPS unconfined compression testing machine is intended primarily
for laboratory use. It was designed specifically to conduct unconfined
compression tests on low strength marine sediments by either strain-
controlled or stress-controlled methods. Allowance was made to facilitate
variation of such factors as range of displacement, loading increment, and
strain rate for future use.

The machine may be configured for either the strain-controlled mode
shown in Figure 2, or the stress-controlled mode shown in Figure 3. In
either configuration the amplifier-indicators and X-Y recorder of Figure 4
are used to respectively amplify and record the load and displacement signals
from the machine. This feature provides a permanent record of precisely
what occurred to the sample during the test. An accurate value of the sedi-
ment shear strength can be computed from this record.

The components of the NPS unconfined compression machine are as follows:

1. Force transducer

2. Displacement transducer

3. Transducer amplifier-indicators

4. Machine screw jactuator

5. Variable speed motor

6. Motor speed controller

7. Structural components

a. Base

b. Lower platform

c. Support columns

d. Upper platform

8. Displacement transducer support bracket

9. Jactuator shaft upper platen

10. Jactuator spacer

11. Shaft extension arms

12. Weighted piston assembly

a. Weight holder

b. Weighted piston shaft

c. Upper platen

27

NCONFINED

Plr KC ooi\) It

TESTING : MACHINE

STRAIN CONTROL

Figure 2. The NPS Unconfined Compression Testing Machine in the
Strain-Controlled Mode

28

Figure 3. The NPS Unconfined Compression Testing Machine in the
Stress-Controlled Mode

29

u
a
*o
u
o
o

CD

■s

CO

CO

w
o

4J
CO

o

•H

c

M

I

u

I

o
o
o

en

4)

o

g

0)

1-1

fa

30

13. Lead discs

14. Ball bushing and pillow block

The components, except for items number 1 through 6 and number 14,
were fabricated by the Machine Facility at the Naval Postgraduate School.
A detailed description of each of these components is given in the following
sections.

FORCE TRANSDUCER

The force transducer shown in Figure 5 is a Series 152 A transducer
manufactured by the Daytronic Corporation of Dayton, Ohio. Its range is
from 0 to 50 pounds, which allows sediment shear strengths of up to 6.6 pounds
per square inch to be measured assuming 2%-inch diameter samples. This maxi-
mum capacity encompasses most shear strength values expected in deep-ocean
marine sediments.

The transducer produces an electrical output proportional to any applied
force or weight. The linearity is 0.2 percent of the transducer range, while
repeatability is 0.1 percent of range. The sensitivity is five millivolts
per volt for rated force at a frequency of 400 Hertz. The deflection of a
dual diaphragm spring, integrally machined from alloy steel, is measured by
a sensitive differential transformer element. This particular type of mechani-
cal design provides rigid lateral probe stability so as to eliminate errors
from side-thrust or non-symmetrical loading. No bearings, pivots or sliding
contacts are incorporated in the transducer, hence it is not subject to
friction errors or wear and provides excellent resolution, repeatability and
long life without hysteresis.

Precision internal construction plus temperature compensation minimize
any zero shift due to temperature changes and allows the use of only 0.005
inches of deflection stroke for full load. The maximum design temperature

31

u

0)

o

3

-o

CO

C
(0

S-i

H

*J

C
0)

E

0)

o
CO
l-»
a

CO

J=
4J

c
cd

u

0)

u

3
T)
CO

c

CO

J-l

H
<U

u
o

e

3

•i-t
fa

32

shift of zero or sensitivity is 0.02 percent of range per degree Fahrenheit.
The ambient temperature range of the transducer is minus 65 to plus 200
degrees Fahrenheit.

Since the system has a high natural frequency, dynamic as well as
static loads can be measured. These dynamic measurements are feasible up to
approximately 20 percent of the natural frequency of the spring-mass system
comprised of the transducer and the supported inertial mass. The natural fre-
quency (in Hertz) is approximately

F = 50
where

\

0.1 + W

L = Nominal rated load of transducer, in pounds.

W = Weight of supported inertial mass, in pounds.

There are mechanical safety stops at either end of travel to prevent
shift of calibration or damage from overloading. The safe load capacity
of the transducer is 150 pounds. Epoxy encapsulation and magnetic shield-
ing of the differential transformer element protects the transducer from
moisture, corrosive atmospheres and external electrical interference.

The transducer receives its power supply from a Model 300D Transducer
Amplifier-Indicator and sends its output signal to the Type 70 Input Module
mounted within the amplifier. A type 22S shielded cable with amphenol con-
nectors joins the amplifier and the transducer. Excitation frequency ranges
from 400 to 10,000 Hertz with a voltage range from two to ten volts.

The force transducer is attached to the lower platform of the unconfined
compression testing machine by four mounting bolts through four %-inch holes
in its 3 9/16-inch diameter base. With its weighing platform installed the
transducer is three inches in height. The weighing platform, which easily screws

33

into a \ inch-28 threaded connection on the top of the transducer, is made
of aluminum and is 3% inches in diameter. The sediment sample, which is
2% inches in diameter, is conveniently placed in the center of the weighing
platform. Once the sample is in place, the force transducer continuously
measures not only the weight of the sample but any applied static or dynamic
force. This measured signal is electrically amplified and sent to an X-Y
recorder where it is displayed on the Y-axis.

DISPLACEMENT TRANSDUCER

The displacement transducer shown in Figure 5 is a Model DS 2000 also
manufactured by the Daytronic Corporation. This provides a continuous out-
put signal voltage which is exactly proportional to the mechanical displace-
ment of the sensing probe. The linear range of displacement of the transducer
is plus or minus one inch and its linearity is within 1.0 percent of cali-
brated range. Transducer sensitivity is 50 millivolts per volt for full
scale displacement at a frequency of 60 Hertz.

The transducer consists of a primary coil and two secondary coils
arranged symmetrically to form a hollow cylinder. A small magnetic iron core,
supported by a non-magnetic rod, is positioned to move axially within the
cylinder in response to the mechanical input to the sensing probe. When the
primary coil is excited by a source of alternating current, and the core is
in the center or null position, the AC voltages induced in the secondary coils
are equal due to the symmetry of coupling between the primary and secondary
coils. The secondary coils are connected in series such that they oppose
each other, hence the induced voltages will cancel in the null position and
there will be no net output voltage. When the core is displaced axially,
one secondary voltage will increase while the other decreases, and a net

34

output signal voltage is produced which is proportional to the magnitude of
displacement from the null position. The phase polarity corresponds to the
direction of displacement from the null position. The output signal volt-
age is sent via a Type 22S shielded cable to a Model 300 D Transducer
Amplifier-Indicator with a Type 70 Input Module. This phase sensitive car-
rier amplifier-indicator provides the greatest accuracy and sensitivity
possible for a differential transformer system.

The coils in the displacement transducer are encapsulated in epoxy,
magnetically shielded and solidly mounted in metal housings. Since the
transducer operates on inductance effects, there are no sliding contacts or
flexing wires. Because of these construction features, the transducer does
not develop noise or open circuits and is extremely resistant to vibrations,
humidity, corrosive atmospheres, and electrical interference. The trans-
ducer is designed to minimize errors from temperature shift of both the zero
and sensitivity controls. The ambient temperature range is minus 65 degrees
Fahrenheit to plus 200 degrees Fahrenheit.

The transducer has an overall length of 12 7/8 inches and a diameter of
7/8 inches. The top of the transducer is provided with a 1^-inch long, 3/4
inch-16 thread such that a locking nut screws on and rigidly secures the
transducer to its mounting bracket in a vertical position. The up-down
motions of the jactuator and weighted piston shafts are mechanically trans-
mitted to the transducer end probe so that the precise position of the up-
per platen of the compression machine is continuously measured, electrically
amplified, and displayed on the X-axis of an X-Y recorder.

TRANSDUCER AMPLIFIER-INDICATOR

The transducer amplifier-indicator shown in Figure 4 is a Model 300 D

35

also manufactured by the Daytronic Corporation. It is a highly sensitive,
solid-state, stabilized, carrier amplifier with a precision indicating
meter. It is completely compatible with and specifically designed to provide
power and receive and amplify signals from either the force transducer or the
displacement transducer. Two amplifier-indicators are used in conjunction
with the unconfined compression testing machine so that both force and dis-
placement signals are continuously received, amplified, and sent to an X-Y
recorder.

The transducer amplifier-indicator comes with a standard recorder out-
put which has an adjustable 5 to 55 millivolt range for full scale output.
Its accuracy is 0.2 percent of the scale for the range on which it is cali-
brated and this accuracy includes effects of line voltage variation, plus or
minus 15 degrees Fahrenheit room temperature variation, and 30 days drift.
The meter output accuracy is 0.5 percent of scale under similar conditions.
The standard meter is six inches, zero on the left, 100 scale divisions, and
scales of 0-20, 0-50, and 0-100 and is equipped with a reversing switch.
Transducer excitation is approximately three volts at 3000 Hertz.

A Type 70 Input Module is used on both amplifier-indicators. This unit
provides nulling, phasing, zeroing, and calibration adjustments. These ad-
justments can be accomplished in a quick and precise manner. The range
selector on this unit offers seven calibrated sensitivity ranges from plus or
minus 0.1 inches full scale to plus or minus 0.001 inches full scale. Pro-
visions are included for operation at multiples of these ranges for longer
stroke measurements. A Transducer Conditioning Selector Switch changes cir-
cuit values in the null control, zero control, and phase compensation cir-
cuits so as to match the electrical characteristics of the transducer selected.
For the 0 to 50 pound force transducer, Position B on the Transducer Condi-
tioning Selector Switch is selected and Position 1 on the Range Selector

36

Switch is used in order to give full scale deflection for ten pounds of force,
This gives a meter accuracy of 0.05 pounds and a recorder output accuracy of
0.02 pounds force. The displacement transducer requires the Transducer Condi-
tioning Selector Switch to be in Position D and the Range Selector Switch in
Position 100. This gives full scale defection for 0.5 inches of displacement,
Thus an accuracy of 0.0025 inches is obtained on the meter and a recorder out«
put accuracy of 0.001 inches is achieved.

The zero control on the module is used to supplement the transducer
mechanical zero adjust or position. The force transducer mechanical zero
adjust is set by the manufacturer but, if nulling can not be accomplished, a
set screw adjustment is provided on the central shaft of the transducer.
This set screw is held in its proper null position by another locking screw
above it and the adjustment is difficult to make. The mechanical zero for
the displacement transducer is the zero position of the end probe necessary
to accomplish nulling of the amplifier. Once nulled, both transducers use
the zero control for precise adjustment of the system zero even at high sensi-
tivities.

The null control for the module provides compensation for quadrature
signal voltages arising from cable capacitance and other sources. Adjust-
ment is quickly accomplished and remains fixed for a given transducer in-
stallation.

The module CAL REFERENCE Control adjusts an internal signal source so
as to simulate the connected transducer at a known value of load or dis-
placement. This source can then be used as a reference standard which
allows rapid checking of calibration at any time.

The power requirements for the amplifier-indicator are 105 to 130 volts,
50 to 400 Hertz, and ten watts. The unit has standard bench mount dimensions

37

of 5% inches high, 17 inches wide, and 9% inches deep. Both the input and
output modules are the plug-in, sliding contact type which allow easy re-
moval for maintenance. One amplifier-indicator is placed on top of the
other and conveniently located next to the X-Y recorder to facilitate moni-
toring of meter indications during testing.

MACHINE SCREW JACTUATOR

The machine screw jactuator is a Model KM-2500-18 manufactured by the
Duff-Norton Company of Charlotte, North Carolina. This unit has a one ton
capacity and is used as the driving shaft for the upper platen on the un-
confined compression testing machine in the strain-controlled mode. A vari-
able speed motor connects to and drives the %-inch, keyed worm gear input
shaft on the jactuator. The worm gear has a standard ratio "of five to one
which moves the keyed output shaft one inch for every 25 turns of the worm
input shaft. The rated torque at full load is 55 inch-pounds. The jactuator
can be controlled exactly for positioning in thousandths of an inch, and its
self-locking feature will hold the load in position without creep.

The output shaft diameter is 3/4 inches and its length is 18 inches.
At the load end of the output shaft a h inch-13-UNC-2A threaded connection,
3/4 of an inch in length, is provided so that the upper platen can be screwed
onto the shaft. Since the output shaft is keyed, no rotation of the shaft
and upper platen occurs.

The closed height of the jactuator is 4% inches and its base size is
2 3/4 x 5 inches. The base is secured to the upper platform of the unconfined
compression machine by means of two, 3/8-inch diameter bolts. An aluminum
spacer 1% inches in height is placed between the jactuator base and the upper
platform so that proper alignment between the jactuator input shaft- and the
motor drive shaft is achieved.

38

VARIABLE SPEED MOTOR

The electric motor used to drive the jactuator is a Type NHS-34RJ
manufactured by the Bodine Electric Company of Chicago, Illinois. It is
a shunt wound, 115 volt DC, ball bearing electric motor rated at 1/15
horsepower. The motor is rated for continuous duty and may be reversed
either while stopped or running. Starting torque for the motor is ap-
proximately 150 percent for full load torque. There are ball bearings on
the motor armature and in the gear head. Its rated ratio is 300 to 1 and
rated speed is 5.7 revolutions per minute.

The overall dimensions of the motor and its gear box is 11 5/8 inches
long, 6 7/8 high, anc1 approximately eight inches wide. The 3/4-inch dia-
meter, keyed output shaft of the motor is connected to the jactuator input
shaft by means of a rigid coupling. The motor base is bolted to the upper
platform of the unconfined compression testing machine by four 3/8-inch
bolts.

MOTOR SPEED CONTROLLER

The Minarik Electric Company of Los Angeles, California, manufactures
the motor speed controller for the variable speed motor. This controller
is specifically designed to operate the Bodine shunt wound motor used on
the unconfined compression testing machine and is the Model W-33. This
particular controller offers excellent regulation, line voltage compensa-
tion and torque control characteristics. A Speed Range Switch on the con-
troller allows selection of either a low or high speed range. In the LO
Position the speed of the motor output shaft can be varied from 0.22 to 6.8
revolutions per minute at a constant torque of 219 inch-pounds. The output
shaft speed can be varied from 0.22 to 10 revolutions per minute at a constant

39

torque of 118 inch-pounds when the HI Position is used. The speed is con-
trolled with a potentiometer mounted with an easily read dial. For a
testing strain rate of two percent per minute, the Speed Range Switch is
placed in the LO Position and the Speed Control Potentiometer is set on 41.
The motor speed can be preset or changed as desired whether the motor is
running or stopped. The controller has a Forward-Brake -Reverse Switch so
that the motor may be instantly started and stopped at any speed setting
under full load. The switch can be left in the Brake Position indefinitely
without overheating the motor.

The controller is made for either 115 or 230 volts AC, 50/60 Hertz in-
put and converts this to the necessary DC voltage, with feedback, for motor
regulation when a changing load or line voltage condition exists. A silicon
controlled rectifier is used for half-wave armature supply. The field
supply is full-wave. A choke-capacitor filtering system provides a better
form-factor which allows a lower motor temperature under constant use, con-
tinuous duty over the entire speed range at rated motor torque, and elimina-
tion of inter-com noise. Dependable solid state circuitry is used in the
controller which provides instant operation and longer life.

The controller is provided with a rugged metal case and a six foot
grounded power supply cable. Key holes on the side of the case allow it to
be easily mounted or removed from the side of the upper platform of the un-
confined compression testing machine. To facilitate testing, the controller
is mounted at the right hand front of the upper platform by means of two
screws. A socket on the back of the controller case accepts the amphenol
connector of the five foot motor cable. A fuse protects the controller
against transient voltages, short circuits and motor overloads.

40

X-Y RECORDER

The X-Y Recorder used during this particular test program was a
Honeywell Model 540. Any quality recorder is however acceptable. The
recorder used should preferably have a one millivolt/division scale and
should be capable of utilizing a 16.5 x 11-inch piece of graph paper with
a ten division per inch scale.

STRUCTURAL COMPONENTS

The structural components of the unconfined compression testing machine
consist of the base, lower platform, upper platform and support columns.
These components have been designed to provide a sturdy, vibrationless
structure upon which to mount the other components. Aluminum was selected
as the material for the base and the upper and lower platforms because it
is lightweight, strong and corrosion resistant. Stainless steel was used
for the columns because of its strength and corrosion properties, and be-
cause of its ready availability. The overall dimensions of the assembled
structural components are 24 inches wide, 26 3/4 inches high and 18 inches
deep.

The base shown in Figure 6 was fabricated from two-inch thick aluminum
plate to provide a solid machine foundation. Eight threaded holes have been
made in the base, four for the support columns and the others to bolt down
the lower platform.

The details of one of the support columns are also shown in Figure 6.
The length of these columns was chosen to provide a height of two feet be-
tween the base and the upper platform. This is to allow easy access to the
weighing platform when handling the sediment sample. Each column screws
into the base, and the top threaded portion of the column penetrates a

41

hole in the upper platform such that weight of the upper platform is sup-
ported by a lip on the column. A nut is then screwed on to the threaded
portion of the column securing the upper platform to the column. The
sturdiness of the columns proved sufficient to eliminate any vibrations
caused by motor rotation.

Shown in Figure 7 is the lower platform. It is fabricated from 3/8-
inch aluminum plate welded to form a five-sided hollow box open at the bot-
tom. Two brackets are welded on both the front and back permitting it to
be bolted to the base. The holes in the brackets are large enough to allow
adjustment of the lower platform so as to insure that the weighing platform
is centered beneath the upper platen. An access hole in the back of the
lower platform facilitates disconnecting the amphenol connector on the dis-
placement transducer and unbolting the force transducer base and displace-
ment transducer support bracket. There are seven holes in the platform top.
Two of these are for displacement transducer support bracket bolts and four
are used to hold the force transducer bolts. The seventh hole allows suf-
ficient space for housing the displacement transducer.

The upper platform, shown in Figure 8, was fabricated from 3/4-inch
aluminum plate and supports the electric motor, jactuator, jactuator spacer,
and the ball bushing. Four holes are provided for mounting the motor, two
holes for mounting the jactuator and jactuator spacer, and two holes for
securing the ball bushing. A large hole allows the passage of either the
jactuator output shaft or the weighted piston shaft. The four additional
holes, previously noted, are for the support columns.

DISPLACEMENT TRANSDUCER SUPPORT BRACKET

The displacement transducer support bracket of Figure 9 bolts to the

42

43

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46

lower platform and provides the support for the displacement transducer.
The two enlarged bolt holes in the bracket allow for lateral movement so
that proper alignment of the displacement transducer end probe can be
achieved. The displacement transducer is secured to the bracket by means
of a lock-nut. The support bracket is constructed from welded strips of
aluminum.

JACTUATOR SHAFT UPPER PLATEN

The jactuator shaft upper platen in Figure 10 is made of lightweight
aluminum finely machined so as to provide a mirror-like finish on its lower
surface. This smooth surface bears on the top of the sediment sample and
is intended to give equal transmission of load throughout the sample. The
upper platen screws on the jactuator shaft and serves to secure the mechani-
cal extension arm to it.

JACTUATOR SPACER

The jactuator spacer shown in Figure 11 is made of aluminum, machined
such that it conforms to the base of the jactuator, and sits between the
jactuator and the upper platform. It allows for proper alignment between
the motor output shaft and the jactuator input shaft.

SHAFT EXTENSION ARMS

The shaft extension arms of both the jactuator shaft and the weighted
piston shaft are displayed in Figure 12. The purpose of these arms is to
provide mechanical extensions which move up and down with their respective
shafts so as to bear on the displacement transducer end probe. Hence, any
shaft movement is exactly transmitted via the mechanical arms to the end
probe. After proper calibration, the precise position of the upper platen

47

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48

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49

50

is continuously known. The extension arm for the jactuator shaft is secured
to the shaft by means of the upper platen. The weighted piston shaft ex-
tension arm is fastened to the weighted piston shaft by a split-ring clamp
tightened by a set screw. Both extension arms are provided with screw ad-
justments used to facilitate displacement transducer calibration.

WEIGHTED PISTON ASSEMBLY

The weighted piston shown in Figure 13 consists of three pieces: the
weight holder, the weighted piston shaft and the weighted piston upper
platen. These can be conveniently assembled on the unconfined compression
testing machine when shifting to the stress-controlled mode of testing.
Each piece was made as light in weight as consistent with strength in order
to reduce the initial load increment placed on the sediment sample to a
minimum. The weight holder was hollowed out both to reduce its weight and
to help retain the small lead discs used for the increment loading. The
weighted piston shaft screws into the weight holder after positioning
through the ball bushing during assembly. The shaft extension arm and the
weighted piston upper platen are normally left attached to the shaft. The
upper platen screws on to the shaft and is constructed similarly to the
jactuator upper platen. The entire weighted piston assembly weighs 1.8
pounds.

LEAD DISCS

Forty 1/8-pound and twenty 1/4-pound lead discs 1 5/8 inches in dia-
meter provide the load increments for the stress-controlled mode of testing.
Combinations of these discs allow selection of the proper load increments
based on the expected value of sediment shear strength. Ideally the sample
should fail somewhere between the application of the tenth and the fif-
teenth equal load increment.

51

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52

BALL BUSHING AND PILLOW BLOCK

The ball bushing used on the unconfined compression testing machine
in the stress-controlled mode is a Model A-81420-SS manufactured by the
Thomson Industries, Inc., of Manhasset, New York. Made of stainless steel,
the bushing precisely guides the 1/2-inch diameter weighted piston shaft
by a unique arrangement of ball bearings providing almost friction-free
linear motion. Binding and chatter of the shaft are eliminated by use of
the bushing and a precision alignment is maintained. Since the bushing
does not depend on an exposed oil film, lubrication is not necessary. The
ball bushing is housed in a Model PB-8-A Pillow Block made by the same
company. This pillow block, built specifically for the ball bushing, pro-
vides a convenient housing and permits adjustment of the shaft alignment
to achieve a vertical position. The pillow block with its installed ball
bushing is mounted to the upper platform of the machine by two mounting
bolts.

53

IV. TEST PROCEDURES

GENERAL

Prior to testing a complete set of detailed test procedures were written
covering sequentially each phase, and during the tests changes were made to
these procedures to ensure their correctness and completeness. The test
procedures contained in the following sections reflect these changes and
are presented in a step-by-step manner for ease in use.

INITIAL ADJUSTMENT OF THE TRANSDUCER AMPLIFIER- INDICATORS

1. The force transducer and the displacement transducer are con-
nected to the Type 70 Input Modules on their respective amplifier-indicators
using Type 22S shielded cables with amphenol connectors.

2. The amplifier-indicator power cables are connected to a 115 volt,
60 Hertz, grounded power source of adequate capacity.

3. A zero check of each amplifier-indicator is made as follows:

a. The Range Selector Switch is turned to the STANDBY Posi-
tion which shorts the amplifier input.

b. The SENSITIVITY Control Knob is turned fully clockwise.
All controls are ten-turn types with friction drive, making it difficult
to determine the end of travel. To position in the midpoint, the knob is
turned at least ten turns in one direction and then turned five turns in
the opposite direction.

c. The METER POLARITY Switch is switched to the NORMAL Position.

d. The POWER Switch is switched to the ON Position and ten
minutes are allowed for stabilization. The meter indication should be with-
in one quarter division from zero. If it is greater than this amount, ad-
justment is made for exactly zero indication using the mechanical adjust-
ment on the face of the meter.

54

4. The TRANSDUCER CONDITIONING SELECTOR Switch is turned to Position
B on the force transducer amplifier-indicator. On the displacement trans-
ducer amplifier-indicator Position D is selected.

5. Null adjustment for each transducer is accomplished as follows:

a. The SENSITIVITY, ZERO, and NULL Control Knobs are position-
ed to the approximate midpoint of their travel. The mechanical input to
each transducer is ascertained to be in the condition desired as zero refer-
ence, i.e., no load on the weighing platform and the displacement trans-
ducer at its mid-point of travel.

b. The RANGE SELECTOR Switch is turned to the NULL Position
converting the amplifier-indicator to a simple, nonphase sensitive AC
voltmeter.

c. The transducer mechanical zero adjustment (or position) is
adjusted to achieve minimum meter reading. This adjustment on the force
transducer requires removing both the weighing platform and the locking
screw from the transducer shaft. The adjustment set screw, found under-
neath the locking screw, is adjusted to give a minimum reading.

d. The NULL Control Knob is adjusted to get a minimum reading
less than that obtained in the previous step.

e. Alternately the mechanical zero adjustment and the NULL
Control Knob are adjusted until no further reduction in meter reading is
obtained. During the adjustment, the SENSITIVITY Control Knob is turned
fully clockwise to get maximum resolution. Minimum null value is usually
less than two divisions. If the mechanical zero adjustment is too coarse
to permit such adjustment, the final stages of the process are carried out

using the ZERO Control Knob in lieu of the mechanical zero adjustment. The
locking screw and weighing platform are then replaced.

55

6. Using shielded cables, the recorder output for the force trans-
ducer amplifier-indicator is connected to the Y-axis of the X-Y Recorder.
Similarly, the recorder output from the displacement transducer amplifier-
indicator is connected to the X-axis of the X-Y Recorder.

7. The X-Y Recorder is connected to a 115 volt, 60 Hertz, grounded
power supply.

8. The amplifier-indicators are now considered to be in adjustment
and ready for their calibration procedure.

CALIBRATION OF THE TRANSDUCER AMPLIFIER-INDICATORS

1. The RANGE SELECTOR Switches on both transducer amplifier-indica-
tors are placed in the STANDBY Position. The POWER Switches are switched
to the ON Position and both amplifier-indicators are allowed five minutes
to warm up.

2. The METER POLARITY Switches on both amplifier-indicators are
checked in their NORMAL Position.

3. The RANGE SELECTOR Switch for the amplifier- indicator connected
to the force transducer is turned to Position 1. Similarly, the RANGE
SELECTOR Switch on the amplifier-indicator connected to the displacement
transducer is switched to Position 100. In this position full scale in-
dication on the force transducer amplifier-indicator meter is ten pounds
while full scale on the displacement transducer amplifier-indicator meter
is 0.5 inches.

4. A piece of graph paper is placed in the X-Y Recorder and the
recorder is placed in its operational mode with its pen up.

5. With the weighing platform installed and no force applied to
it, the force transducer meter and the recorder Y-axis are checked in

56

the zero position. If they are not on zero, the ZERO Control Knob is ad-
justed to give proper meter zero and then the recorder zero adjustment is
made with its Zero Adjustment Knob.

6. To calibrate the force transducer amplifier-indicator a known
weight of exactly five pounds is placed on the weighing platform and both
the meter and recorder indications are read. If the meter does not indicate
five pounds, the SENSITIVITY Control Knob is adjusted to give a precise
indication of five pounds. The Range Selector Switch is shifted to the CAL
Position and the CAL REFERENCE Control Knob is adjusted to give exactly full
scale indication. The Range Selector Switch is then shifted back to Posi-
tion 1 and the recorder Y-axis is checked to insure it is indicating five
pounds. If it is not indicating properly, a recorder adjustment is made.
This requires simultaneous adjustment of the 5-55 millivolt Recorder Output
Adjustment Knob found on the back of the amplifier-indicator and the recorder
Y-axis zero adjustment to achieve a proper linear signal into the recorder.
If linear calibration on the recorder still is not obtained, the recorder
Y-axis variable adjustment is used to make the final calibration. The force
transducer amplifier-indicator is now considered calibrated.

7. The upper platen of the unconfined compression testing machine is
positioned to give a dial caliper indication of 4.5 inches between it and
the weighing platform. If the machine is rigged in the strain control mode,
the SPEED RANGE Switch on the motor controller is switched to the HIGH
Position and the maximum speed setting on the SPEED CONTROL Potentiometer

is used to facilitate positioning the platen. The displacement transducer
amplifier-indicator meter and the recorder X-axis indications are checked
in the zero position. If not on zero, the screw adjustment on the shaft
extension arm which moves the displacement transducer end probe is adjusted

57

to give a meter indication of zero. The recorder X-axis is then adjusted
to zero.

8. Using the dial caliper for indication, the upper platen is placed
precisely five inches above the weighing platform. The amplifier-indica-
tor meter is now checked. If not on plus 0.5 inches (full scale indication),
the SENSITIVITY Control Knob is adjusted to give a reading of precisely 0.5
inches. This plus 0.5 inches corresponds to a sample height of five inches.
The Range Selector Switch is shifted to the CAL Position and the CAL REFER-
ENCE Control Knob is adjusted to give exactly full scale indication. The
Range Selector Switch is shifted to Position 100 and the recorder X-axis
is checked to insure it is indicating its zero position corresponding to a
sample height of five inches. If the recorder does not indicate this dis-
placement, a recorder adjustment is made. This requires an adjustment similar
to that made in Step 6, only using the Recorder Output Adjustment Knob for
the displacement transducer amplifier-indicator and the X-axis zero adjust-
ment. The displacement transducer amplifier-indicator is now considered
calibrated.

MACHINE CONVERSION TO THE STRAIN -CONTROLLED MODE

1. The variable speed motor cable is connected to the motor speed
controller and the controller is plugged into a 115 volt, 60 Hertz, grounded
power supply.

2. The jactuator spacer is placed in position on the upper platform.
The jactuator shaft without its upper platen installed is placed through
the spacer and the upper platform until the jactuator base rests on the
spacer.

58

3. The jactuator input shaft is then connected to the rigid coupling
normally left on the motor output shaft. The jactuator input shaft keyway
is aligned to receive the rigid coupling set screw. The set screw is
tightened. It is found that this is a critical step because any relative
motions between the shafts cause a variation in load.

4. Both mounting bolts are installed through the jactuator base,
spacer and upper platform. Their nuts are tightened, securing the jactuator
to the upper platform.

5. The jactuator shaft extension arm and the upper platen are instal-
led on the jactuator shaft. The upper platen is tightened with the exten-
sion arm screw adjustment aligned on the displacement transducer end probe.

6. The calibration procedure for the transducer amplifier-indicators
is conducted to check on the system calibration. Once the upper platen is
placed at a height of 4.5 inches above the weighing platform and the ex-
tension arm screw adjustment is adjusted to give zero indication on the
displacement transducer amplifier-indicator meter, the system is generally
found to be in calibration.

7. The upper platen is positioned to a height of approximately 5.1
inches above the weighing platform using the recorder indication.

8. The SPEED RANGE Switch on the motor speed controller is switched
to the LO Position. The SPEED CONTROL Potentiometer is set at 41 which
corresponded to a rate of strain of 0.1 inches per minute or two percent
per minute for a five-inch sample. The machine is now ready to receive
the sample.

MACHINE CONVERSION TO THE STRESS -CONTROLLED MODE

1. The unconfined compression testing machine is unrigged from the
strain-controlled mode by reversing the order of its assembly.

59

2. The ball bushing pillow block is tightly bolted to the upper
platform using its two mounting bolts.

3. The weighted piston shaft, with its extension arm and upper
platen already attached, is put in position up through the ball bushing.
The weight holder is screwed tightly on the upper end of the shaft.

4. The weighted piston assembly is manually raised and positioned
so that the extension arm screw adjustment is centered on the displacement
transducer end probe.

5. A calibration check is made on the displacement transducer
amplifier-indicator. Once the calibration check is made, a pin is placed
through a hole in the weighted piston shaft and the assembly is lowered
until the pin rests on the ball bushing. This positions the upper platen
approximately 5.1 inches above the weighing platform. The machine is ready
to receive the sample.

PREPARATION OF THE UNDISTURBED SAMPLE

1. The exterior surface of the core plastic liner is wiped clean
and dry.

2. Starting at the top of the core, the plastic liner is marked
with a waterproof marking pen at the desired cutting locations. A sequ-
ence of one three-inch section followed by two five-inch sections is
repeated throughout the length of the core.

3. The cutting guide collar (Smith and Nunes, 1964), shown in
Figure 14, is placed at the first cutting mark. The guide clamp is tighten-
ed.

4. Using the Weller D-550 soldering gun and the modified cutting
tip (Smith and Nunes, 1964) also shown in Figure 14, the plastic liner
is circumferentially cut at the first position.

60

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5. A coping saw equipped with a piano wire for a blade is used to
cut carefully through the core.

6. Steps 3, 4, and 5 are repeated for the n?xt cutting position.

7. The three-inch section is carefully removed, the bottom of its
plastic liner capped, and the sediment shear strength is measured with

a vane shear apparatus (Heck, in press) without removing the sediment from
the plastic liner.

8. Step 6 is repeated for the following five-inch section.

9. The five-inch section is removed and immediately placed on a
spatula in a vertical position. This prevents the sediment from coming
out of the core plastic liner.

10. The plastic liner is placed in a clamping device and held there
while a hand ejection piston is used to carefully extrude the sample with
a minimum of disturbance. The sample is maintained on the spatula during
this step and very little disturbance occurrs.

11. Using the spatula, the sample is placed in the center of the
force transducer weighing platform and the spatula is removed.

12. The X-Y Recorder Operating Switch is placed in the PEN Position.
The recorder graph indicates the sample weight and is ready for testing.

TESTING IN THE STRAIN-CONTROLLED MODE

1. The Motor Controller Operating Switch is turned to the FWD
Position. This causes the upper platen to be driven downward at an axial
rate of strain of two percent per minute. Care is taken to insure that
good contact is made between the upper platen and the sample.

2. The X-Y Recorder graph is checked to see that a good reading
is being made.

62

3. When a distance of at least 20 percent of the initial sample
height is traversed by the upper platen, the Motor Controller Operating
Switch is turned to the BRAKE Position.

4. This is considered the end of the test and the X-Y Recorder
Operating Switch is placed in its OPERATE Position which lifts the pen.

5. The Motor Controller Operating Switch is turned to the REVERSE
Position, the SPEED RANGE Switch placed in the HI Position, and the SPEED
CONTROL Potentiometer turned to its maximum setting. This raises the
upper platen off the sample.

6. When the upper platen is about 5.1 inches above the weighing
platform as indicated on the recorder, the Motor Controller Operating Switch
is turned to the BRAKE Position.

7. Removal of the sample is accomplished by carefully unscrewing the
weighing platform from the force transducer and carrying the platform with
the sample on it to a desired location where the sample is removed.

8. The weighing platform and the upper platen are wiped clean and
the platform reinstalled on the force transducer.

9. The X-Y Recorder Operating Switch is placed in its load position.
This allows removal of the graph paper with its load versus sample height
curve. A new piece of graph paper is installed. The recorder is placed
in its operational mode with its pen up ready for the next test.

TESTING IN THE STRESS -CONTROLLED MODE

1. Based on the expected value of sediment shear strength, the
weight increment of loading is chosen. Generally, 1/4-pound or 3/8-pound
increments are used. These increments are made up of combinations of the
1/4-pound and 1/8-pound discs.

63

2. The timer is plugged into a 115 volt, 60 Hertz, grounded, power
supply and turned on.

3. The pin is removed from the weighted piston shaft and the shaft
slowly lowered until the upper platen rests evenly on the top of the sedi-
ment sample. This is considered the first load increment. The time at
which contact is made with the sample is noted.

4. After the first load increment, the previously chosen increment
of weight is placed on top of the weight holder at 30 second intervals.

5. Incremental loading is continued until the upper platen has
traveled at least 20 percent of the initial sample height.

6. The X-Y Recorder Operating Switch is placed in its OPERATE Posi-
tion which lifts the pen. It is then placed in its LOAD Position.

7. The lead discs are removed from the top of the weight holder.
The weighted piston shaft is slowly raised until the upper platen is clear
of the sample. The shaft is then pinned in its starting position.

8. Sample removal and the replacing of graph paper in the recorder
are accomplished in a manner identically described in the testing pro-
cedure for the strain-controlled mode of operation.

64

V. TEST RESULTS

On April 23, 1970, a sediment sampling program was carried out from
the USNS BARTLETT (T-AGOR-13). The vessel departed from the port of
Oakland and proceeded southwesterly along the continental slope between
San Francisco and Monterey. At the ten locations along the track shown
in Figure 15, the ship was stopped and an Ewing gravity corer with 450
pounds of weight was used to obtain a core. The sediment samples varied
in length from 39 to 71.5 inches. The depth of water at the core locations
ranged from 340 to 1870 fathoms. In each case the core liner was removed
from the core barrel, capped, sealed and placed vertically in a specially
constructed storage drum filled with sea water. This storage drum was
carefully removed from the ship upon return to port and placed in storage
until the test program commenced on the 3rd of August. A summary of the
coring data is presented in Table I. All cores were dark green colored
clays, with the exception of Core 1W and Core 2W which both contained some
sand.

Between August 3rd and August 5th the ten cores were analyzed as
follows. The top three-inch section was removed from the core and tested
on the NPS vane shear apparatus (Heck, in press) to determine a vane shear
strength value. This three-inch section was then remolded to determine
its sensitivity and a portion was used to obtain the water content. A
summary of the values computed for the vane shear strength, sensitivity,
and water content for each sample appear on Table II through Table XI.
Two five-inch sections were then removed from the core and tested on the
NPS unconfined compression testing machine. The first five-inch section
was tested using the strain-controlled mode and the second five-inch

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77

section the stress-controlled mode. The detailed test procedures described
in the previous section were followed. In each case a recording of load
versus sample height was made. The load values appearing on the record
include the weight of the sample. Arrows were inserted on the curves shown
in Figure 16 through Figure 35 to indicate sample height and sample weight.
This sequence of testing was repeated throughout the length of each core.
In conducting the strain-controlled tests on Core 1W, the rate of strain
exceeded the recommended maximum value and hence the data for this parti-
cular test sample is considered questionable.

Figure 16 through Figure 35 depict the original load - sample height
curves produced. Each figure combines those sections for one core which
were tested in a similar mode of machine operation. It is believed signi-
ficant that in all tests a point on each load - sample height plot is
reached where the curve increases in a linear manner. Th<i point at which
such a linear increase begins is termed the linear point and its position
is marked on each curve. Every observed sample physically sheared at ap-
proximately this location on the curve. Evidently the sample shears when
the rate of change of load with respect to sample displacement becomes con-
stant. This is considered important for a number of reasons. It would
eliminate the necessity for continuing the test once linearity of the load -
sample height curve is established and, if a large number of tests were
being conducted, the time spent testing each sample would be reduced.
Also, only one set of calculations would have to be made to compute the
shear strength value. The value of load and displacement of the sample
at the linear point would be used for these calculations. The sediment
shear strength was computed using the value of load and sample displacement
at the linear point and this is considered the linear strength value.

78

L
0
A
D

?
0
U
N
D
S

3-8 INCHES

5:0 "33" 4:0

SAMPLE HEIGHT (INCHES) ?i^™ i*

79

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0
A
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?
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U
N
D
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.8

.7

_6

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.6

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SCALE
SHIFT

CORE IW
STRESS CONTROL

8-13 INCHES

21-26 INCHES

34-39 INCHES

fWU

47-52 INCHES

X= LINEAR POINT
0=20% POINT

""• —»^ r

5:0 ' 4.5 4:0 -

SAMPLE HEIGHT (INCHES) Fi-ure 17

80

3-8 INCHES

L
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A
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.5
.4
J3
2.

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.3

.2

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3

.6

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ID

16-21 INCHES

29-34 INCHES

42-47 INCHES

CORE 2W

STRAIN CONTROL

55-60INCHES

X; LINEAR POINT
0=20% POINT

5.0 4.5 4.0

SAMPLE HEIGHT (INCHES) ?i^e 18

81

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?
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U
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.0

.3
.2

.1

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.8

.6

.4

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47-52 INCHES

CORE 2W

STRESS CONTROL

60-65 INCHES

X= LINEAR POINT
0=20% POINT

5.0 4.5 4.0

SAMPLE HEIGHT (INCHES)?***™ 19.

82

3-8 INCHES

.0
.3

16-21 INCHES

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3

.2

J

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3

.2

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.4

3

_2

J

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29-34 INCHES

42-47 INCHES

CORE 3W

STRAIN CONTROL

55-60 INCHES

X=LINEAR POINT
0=20% POINT

t _•

5.0 475 4!0

SAMPLE HEIGHT (INCHES) ?irure 20.

83

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0
A
D

?
0
U
N
D
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.2

_o r

3
.2
J

_0
.5
_4
3
.2

8-13 INCHES

21-26 INCHE:

34-39 INCHES

47-52 INCHES

CORE 3W
STRESS CONTROL

60-65 INCHES

X=LINEAR POINT
0=20% POINT

5.0 4.5 4.0

SAMPLE HEIGHT (INCHES)"irr^e 21

84

L
0
A
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?
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U
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3
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J
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.5
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.6
.5
A
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.2
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.6
.5
1-4
.3
.2
J
.0

3-8 INCHES

16-21 INCHES

29-34 INCHES

CORE 4W

STRAIN CONTROL

42-47 INCHES

X--LINEAR POINT
0=20% POINT

5.0 4.5 4.0

SAMPLE HEIGHT (INCHES) Finire 22.

85

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0
A
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0
U
N
D
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.3

.2

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.5

_4

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L2

.1

.0

.5

.4

.3

.2

.1

LO

.6

.5

.4

.3

.2

J

.0

8-13 INCHES

21-26 INCHES

34-39 INCHES

CORE 4W

STRESS CONTROL

47-52 INCHES

X=LINEAR POINT
0=20% POINT

5.0 4.5 4.0

SAMPLE HEIGHT (INCHES) ?i^re 25

86

L
0
A
D

?
0
U
N
D
S

5.0 ' 4.5 ' " ' 4!0

SAMPLE HEIGHT (INCHES)?i£^e 24

87

L
0
A
D

?
0
U
N
D
S

CORE 5W

60-65 INCHES

X=LINEAR POINT
0=20% POINT

STRESS CONTROL

4.5 ' 4!0

SAMPLE HEIGHT (INCHES) F±^Te ^

.0

3

.2

J

.0

3-8 INCHES

6-21 INCHES

L
0
A
D

?
0
U
N
D
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.8

-7

.6

.5

.4

.3

.2

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.5

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29-34 INCHES

CORE 6W

STRAIN CONTROL

42-47 INCHES

X=LINEAR POINT
0=20% POINT

"] r

5:0 475 ' ■ 4:0

SAMPLE HEIGHT (INCHES) FiffUre 26-

89

.3

.2

J

.0

8-13 INCHES

L
0
A
D

?
0
U
N
D
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.6
.5
A

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.7

.6

J5

.4

3

.2

J

.0

CORE 6W
STRESS CONTROL

21-26 INCHES

J^^w/VH

34-39 INCHES

X=LINEAR POINT
0=20% POINT

SO 45 4!0

SAMPLE HEIGHT (INCHES) Figure 27.

90

.4
.3
.2

.0

3-8 INCHES

L
0
A
D

?
0
U
N
D
S

jj

.2

0

.6

.5

_4

.3

.2

J

.0

CORE 7W
STRAIN CONTROL

16-21 INCHES

29-34 INCHES

X^ LINEAR POINT
0=20% POINT

5.0 4.5 4.0

SAMPLE HEIGHT (INCHES)-i-ure 28.

91

.5

.4

.3

.2

J

.0

8-13 INCHES

L
0
A
D

?
0
U
N

D
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.7

_6

,5

.4

.3

_2

.1

.0

.6

.5

.4

.3

.2

J

_0

CORE 7W

STRESS CONTROL

21-26 INCHES

34-39INCHES

X= LINEAR POINT
0=20% POINT

5:0 43 ^ ^ 4:0

SAMPLE HEIGHT (INCHES) Fi^re 29.

92

3
.2
.1

.0

3-8 INCHES

L
0
A
D

?
0
U
N
D
S

.6

A

J
_0

16-21 INCHES

CORE 8W

STRAIN CONTROL

.4

.3

.2

J

.0

29-34 INCHES

X- LINEAR POINT
0=20% POINT

■ »

i ; i — i

4.5 4.0

SAMPLE HEIGHT (INCHES) Figure 30

93

A

.3

2.

J

.0

8-13 INCHES

L
0
A
D

?
0
U
N
D
S

_6

_5

_4

3

.2

J

.0

21-26 INCHES

CORE 8W
STRESS CONTROL

^/W

34-39 INCHES

X^ LINEAR POINT
0=20% POINT

5.0 4.5 4.0

SAMPLE HEIGHT (INCHES) Figure 31.

94

.4

.3

_2

J

.0

3-8 INCHES

L
0
A
D

?
0
U
N
D
S

.5

_4

.3

.2

J

.0

.6

.5

.4

.3

.2

J

.0

_4

.3

.2

J

.0

6-21 INCHES

29-34 INCHES

CORE 9W

STRAIN CONTROL

42-47 INCHES

X= LINEAR POINT
0=20% POINT

5.0 4.5 4.0

SAMPLE HEIGHT (INCHES) Figure 32

95

L
0
A
D

?
0
U
N
D
S

.5

A

,3

.2

.1

.0

.7

.6

.5

_4

.3

.2

J

_0

8-13 INCHES

21-26 INCHES

CORE 9W

STRESS CONTROL

.5

.4

.3

.2

.1

_0

rX-f

34-39 INCHES

X^ LINEAR POINT
0=20% POINT

5.0 4.5

4.0

SAMPLE HEIGHT (INCHES) Figure 33.

96

.3
.2
.1

.0

3-8 INCHES

L
0
A
D

?
0
U
N
D
S

_o

6-21 INCHES

CORE IOW
STRAIN CONTROL

_5

_4

.3

_2

J

_0

29-34 INCHES

X= LINEAR POINT
0=20% POINT

5:0 ^ 4:5 ^ ^470 ^'

SAMPLE HEIGHT (INCHES) T±^re 54

97

L
0
A
D

?
0
U
N
D
S

.5

.4

.3

_2

J

.0

_7

_6

.5

A

.3

.2

J

.0

J

_6

.5

_4

.3

.2

J

_0

8-13 INCHES

21-26 INCHES

CORE IOW

STRESS CONTROL

34-39INCHES

X= LINEAR POINT
0=20% POINT

5:0 4:5 4:0

SAMPLE HEIGHT (INCHES) Fi^re 55

98

Two shear strength computations were made. The first included the sample
weight as part of the load value and the second neglected the sample weight.
This was done to ascertain the effect of sample weight on the shear strength
determination. The values of linear strength and the strain at which the
linear point occurred are both listed for each sediment sample in Table II
through Table XI.

Using the initial sample height as indicated on the load - sample
height curve, a 20 percent displacement height was computed and this point
was also marked on the curve as the "20 percent point." Two shear strength
values were computed using the values of load and sample displacement at
this "20 percent point," one without the sample weight and one with the
weight included. Tabulated results of these calculations are also in-
cluded in Table II through Table XI.

Close examination or: the load - sample height curves of Figure 16
through Figure 35 shows that extremely smooth curves are made when conducting
the strain-controlled mode of testing. Load and sample displacement values
from these curves gave calculated results producing smooth stress - strain
curves.

Curves made in the stress-controlled mode of testing produced differ-
ent results. Due to friction losses and because a portion of the load was
required to move the displacement transducer end probe, the weight of the
load increment was not entirely transmitted to the sample. This is shown
on the curves. Also, between load increments, there were many changes in
the load applied to the sample caused by either friction or sample shear.
Vibrations of the machine and electrical interference from surrounding
equipment were not involved. This was indicated by the initial smooth
portion of the curve where only the sample weight was recorded as the
weighted piston assembly was lowered to contact the sample.

99

The frictional losses come from two sources. The first involves the
contact between the weighted piston shaft and the ball bushing. A second
source, considered negligible, results from the movement of the displace-
ment transducer end probe. The ball bushing was specifically used on the
machine to minimize friction loss and is considered to be the best practi-
cal arrangement. Incremental shearing of the sample produced the remaining
changes in load and this shearing is uniquely depicted on the load versus
sample height recordings. In some cases this shearing was physically
observed. The fact that the load unpredictably did change, sometimes as
much as the load increment itself, caused greater point scatter on the
stress versus strain curves during testing. This results in a reduced ac-
curacy of the shear strength value in the stress-controlled, mode of testing,

The stress-strain curves shown in Figure 36 through Figure 55 were
plotted, following standard practice. Each figure contains the curves for
the samples of that core which were tested in a similar mode. Values of
stress and strain were calculated at every 1/10-inch displacement of sample
height. Two curves were plotted for each sediment sample. The upper curve
includes the sample weight in the stress calculations, whereas the lower
curve neglects the sample weight. Faired curves were drawn through the
plotted points. The maximum stress value on each curve is marked. Shear
strength calculations were made using the maximum stress on the stress-
strain curve and includes sample weight. These maximum shear strengths
and the percent strain at which they occurred are listed in Table II
through Table XI.

The stress-strain curves plotted in Figures 36 through 55 all show
the general tendency of leveling off to a constant value of stress. There
were only two curves that dropped off sharply in classic manner. The first

100

s

T
R

E
S
S

P
S

3-8 INCHES

INCHES

INCHES

CORE IW
42-47 INCHES

X=MAXIMUM

©= MAXIMUM WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.)"*-*-

101

s

T
R

E
S
S

P
S

-13 INCHES

-26 INCHES

9INCHES

CORE IW
47-52 INCHES

X= MAXIMUM

0= MAXIMUM WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.)?1?ure"7-

102

s

T
R

E
S
S

P

S

-8 INCHES

16-21

INCHES

-34 INCHES

47 INCHES

5-60 INCHES
CORE 2W

UM

UM WITHOUT WEIGHT

0~ .0*5 .l'0 TB 1?Q ^25 .3'0

STRAIN (IN. PER IN.) Fieure38

103

s

T
R

E
S
S

P
S

-13 INCHES

-26 INCHES

34-39 INCHES

47-52 INCHES

CORE 2W
60-65 INCHES

X=MAXIMUM

®= MAXIMUM WITHOUT WEIGHT

0 .0 5

0 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.)

Figure 39,

104

s

T
R

E
S
S

P

s

3-8 INCHES

6-21 INCHES

29-34 INCHES

CORE 3W

-47INCHES

55-60 INCHES

MAXIMUM

MAXIMUM WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.)1— 40-

105

s

T
R

E
S
S

?
S

21-26 INCHES

34-39 INCHES

8-13 INCHES

-52 INCHES

E 3W
NCHES

T WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.)7™41-

106

s

T
R

E
S
S

P
S

-8 INCHES

16-21 INCHES

29-34 INCHES
CORE 4W

42-47 INCHES

UM WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.)F^,re42-

107

s

T
R

E
S
S

?
S

8-13 INCHES

21-26 INCHES

-39 INCHES

CORE 4W

47-52 INCHES

IMUM
MUM WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.)11-^13-

108

INCHES

16-21 INCHES

29-34 INCHES

CORE 5W

42-47 INCHES

55-60
INCHES

MAXIMUM

MAXIMUM WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.) i,:re/-

109

s

T
R

E
S
S

P
S
I

8-13 INCHES

-26 INCHES

34-39 INCHES

CORE 5W

47-52 INCHES

0-65 INCHES

MUM

MUM WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.) Pi—45-

no

3-8 INCHES

16-21 INCHES

29-34 INCHES

CORE 6W

-47 INCHES

WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.)7—0^

in

s

T
R

E
S
S

P

s

8-13 INCHES

21-26 INCHES

CORE 6

34-39 INCHES

X=MAXIMUM

®= MAXIMUM WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.)

Figure 47.

112

CHES

16-21 INCHES

CORE 7W

29-34 INCHES

X=MAXIMUM

®= MAXIMUM WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.) ^fiA8-

113

s

T
R

E
S
S

P
S

-13 INCHES

-26 INCHES

CORE 7W

NCHES

UT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 ,3 0

STRAIN (IN. PER IN.)

Figure 49.

114

INCHES

16-21 INCHES

CORE 8W

29-34 INCHES

MUM

MUM WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.) Figure 50,

115

s

T
R

E
S
S

?
S

.0
.6.
.4
.2
0.
.5
.4
.3.
.2

8-13 INCHES

-26 INCHES

CORE 8W

-39 INCHES

WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.) Fisure51,

116

-8 INCHES

16-21 INCHES

29-34 INCHES

CORE 9W
47INCHES

WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.)— r^

117

8-13 INCHES

-26 INCHES

CORE 9W

-39INCHES

HOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .3 0

STRAIN (IN. PERIN.)Fi

Lgure 53.

118

16-2! INCHES

INCHES

CORE IOW

29-34 INCHES

MUM

MUM WITHOUT WEIGHT

0 .0 5 .10 .15 .2 0 .2 5 .30

STRAIN (IN. PER IN.)F±sure54-

119

s

E
S

P

s

4

.3
.2

0

.6

.5

.4

.3

.2

.1

0

.7

-13 INCHES

1-26 INCHES

CORE IOW

-39 INCHES

OUT WEIGHT

0 .0 5

0 .15 .2 0 .2 5 .3 0

STRAIN (IN. PER IN.)

Figure 55.

120

occurred on the 3- to 8-inch sample for Core 1W, and is perhaps invalid.
The curve for the 34- to 39-inch sample for Core 9W dropped off at a point
beyond 20 percent strain. The flattening of the remaining curves begins
in the vicinity of the linear point.

A comparison was made for each sample between the linear strength
with and without sample weight and the maximum strength on the faired
stress-strain curve. The 20 percent strength with and without sample weight
was also compared to the maximum faired curve strength. The results are
given in percent in Table XII and Table XIII. An example of these results
is the 55-60 inch section of Core 5W. In this section the ratio of the
linear strength which includes the sample weight to the maximum faired
curve strength is 99.2 percent. Without the sample weight included, this
ratio is 96.4 percent. The ratio of the 20 percent strength with the
sample weight to the maximum faired curve strength is 99.4 percent. This
ratio is 100.0 percent neglecting sample weight. Without including Core
1W, 70 sediment samples were analyzed. Of the four shear strength compari-
sons made for each sample (a total of 280) only 13 differed by greater than
10 percent from the faired curve strength. Only 42 were outside of a five
percent band. Fifty-four shear strength values exactly equaled the faired
curve strength. Of importance is the fact that there was no preference
as to whether the linear or the 20 percent strength more closely approxi-
mated the faired curve strength. The shear strength at the linear point
was therefore considered to be the actual sediment shear strength.

A primary design goal of the NPS unconfined compression testing machine
was inclusion of the sample weight as part of the measured load. Sample
weight was considered as an integrating type load, with the maximum load
due to the weight of the sample itself being at the bottom of the test

121

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section. Since the samples tested each weighed approximately one pound,
this weight load ranged from 10 to almost 50 percent of the failure load,
with an average of about 20 percent. This is considered significant.

To verify the importance of sample weight as part of the failure load,
each sample was inspected to determine where failure occurred. The results
are tabulated in Table XIV. Examination of this table indicates that of
the 70 samples tested (excluding Core 1U) seven samples failed at the top
while 52 samples failed at the bottom. The remaining 11 samples failed at
both the top and the bottom. There were no failures through the center por-
tion of the samples. Although variations existed, most cores increased
slightly in shear strength with depth of core as shown by Figure 56 through
Figure 65. This implies that the bottom part of a sample should have been
very slightly stronger than the top, and the failure plane should therefore
have originated at the top. Since this was generally not the case, the
sample weight appears to have been a sufficient added load to cause failure
at the bottom of the sample.

The angle of the failure plane with respect to the horizontal is also

tabulated in Table XIV for each sample. Typical failed samples are shown

in Figure 66. With the exception of two samples, all 78 failed at an angle

of 60 + 4 degrees. Fifty of the samples failed at exactly 60 degrees.

This indicates a friction angle 0 of 30 degrees for most samples since

6 = 45° + \

where

6 = Angle of failure with respect to the horizontal.

This is considered of appreciable consequence in that the friction angle,

as noted previously, has always been assumed equal to zero for marine

sediments. This assumption apparently is not valid and considerable solid

124

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125

CORE NO: 1W

SHEAR STRENGTH ( ps i )
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

A VANE SHEAR
0 LINEAR
Q LINEAR-

WITHOUT WEIGHT

Figure 56.

126

CORE NO:

SHEAR STRENGTH (ps i )
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

A VANE SHEAR
0 LINEAR

Q LINEAR-

WITHOUT WEIGHT

127

Figure 57

CORE NO: 3W

SHEAR STRENGTH ( p s i )
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

VANE SHEAR
LINEAR

LINEAR-

WITHOUT WEIGHT

Figure 58.

128

CORE NO: 4

SHEAR STRENGTH (ps i )
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0,8 0.9 1.0

10
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Figure 59.

129

CORE NO; 5W

SHEAR STRENGTH (ps i )
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10
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Figure 60.

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CORE NO:

SHEAR STRENGTH ( ps i
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Figure 61.

131

CORE NO: 7

SHEAR STRENGTH ( P$ i )
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Figure 62

132

CORE NO: 8 W

SHEAR STRENGTH ( P« i )
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Figure 63.

133

CORE NO: 9

SHEAR STRENGTH ( ps i )
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Figure 64.

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CORE NO: (QW

SHEAR STRENGTH (ps i )
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136

friction does appear to exist. If the friction angle is 30 degrees, then
the utilization of sediment shear strength values would have to take this
0-angle into account for all purposes. For example, it would appreciably
affect present methods of computing the bearing capacity of sea floor
materials. The results of this investigation indicate that it is manda-
tory that triaxial tests be conducted on marine sediments to confirm the
existence of this solid friction and to give comparison data for the un-
confined and vane shear methods of testing.

Figure 56 through Figure 65 show the linear strength, linear strength
without weight, and vane shear strength plotted against core depth. With
the exception of Core 1W and two low peaks in the linear strength curves
of Core 2W, all curves are remarkably similar in shape. The vane shear
strength curves compare more favorably with the linear strength curves
which include sample weight than to those without sample weight. In
Cores 6W through 10W the vane shear curves were slightly higher in value
than the linear strength curves. Perhaps this is due to slight distur-
bance on removing the samples from the core liners. The Core 3W and Core
4W curves are almost identical.

The agreement between the unconfined compression shear strength curves
and the vane shear strength curves is considered important. It shows that
both methods are accurate enough to concur in measuring the variations in
cohesion with sample depth. Additionally, confidence is gained in the
values of shear strength obtained when using a vane shear device because
they compare so closely to those measured using the classical unconfined
compression test.

137

VI. CONCLUSIONS

The sediment shear strength computed from the linear point of the
load - sample height curve as recorded by the NPS unconfined compression
testing machine represents the actual sediment strength as measured by
this test device.

Friction losses and load changes due to incremental sample shear
could represent a large fraction of the failure load of low strength marine
sediments. To account for these variations, unconfined compression testing
apparatus that test in the stress-controlled mode should measure the actual
load being applied to the sample.

The strain-controlled mode of the NPS unconfined compression testing
machine produces a smooth load - sample height curve. An accurate linear
strength can easily be computed from this curve. This mode of testing
should be used whenever possible.

Sample weight can represent a large fraction of the total load to
cause failure on low strength marine sediments. This should be considered
in the calculations for sediment shear strength.

The friction angle for the marine sediments tested on the NPS un-
confined compression testing machine averaged 30 degrees. Calculations for
sediment shear strength have heretofore assumed that friction angle was zero,
This aspect appears to require considerable further study.

Sediment shear strengths obtained from the NPS unconfined compression
testing machine are in close agreement with those obtained using the NPS
vane shear apparatus, and hence confirm the usefulness of vane shear
equipment for measurements of cohesion.

138

VII. RECOMMENDATIONS FOR FURTHER RESEARCH

The following areas associated with the NPS unconfined compression
testing machine are recommended for additional research:

1. Determine quantitatively the effects of varying the rate of
strain, sample height, and load increments.

2. Develop a device that removes the sediment sample from the core
liner in the same direction as the sample entered the liner as a means of
further reducing sample disturbance.

3. Closely examine the previously widely adopted concept that the
0-angle for deep sea sediments is close to zero.

139

BIBLIOGRAPHY

American Society for Testing and Materials, Procedures for Testing Soils,
4th ed. , p. 252-255, 1964.

Bryant, W. R. , Cernock, P., and Morelock, J., "Shear Strength and Consoli-
dation Characteristics of Marine Sediments from the Western Gulf of
Mexico," in Marine Geotechnique , edited by A. F. Richards, p. 41-64,
University of Illinois Press, 1967.

Grim, Ralph E. , Applied Clay Mineralogy, McGraw-Hill Book Company, Inc.,
New York, 1962.

Heck, J. R. , Engineering Properties of Sediments in the Vicinity of Guide
Seamount, M. S. Thesis, Naval Postgraduate School, in press.

Hough, B. K. , Bftsic Soils Engineering, 2nd ed. , p. 90-101, The Ronald
Press Company, New York, 1969.

Inderbitzen, A. L. , and Simpson, F. , "A Comparison of the Test Results
of Vane and Direct Shear Tests Made on Recent Marine Sediments,"
Lockheed Missiles and Space Company Report LMSC 694965, 1969.

Keller, G. H. , "Shear Strength and Other Physical Properties of Sediments
from Some Ocean Basins," Proceedings of the Conference on Civil
Engineering in the Oceans, American Society of Civil Engineers, 1968.

Kessler, R. S. , and Stiles, N. T., "Comparison of Shear Strength Measure-
ments with the Laboratory Vane Shear and Fall-Cone Devices," Naval
Ocermographic Office Informal Report No. 68-75, 1968.

Lambe, William T. , Soil Testing for Engineers, p. 110-146, John Wiley
and Sons, Inc., New York, 1951.

Minugh, E. M. , A Versatile Vane-Shear Apparatus, M. S. Thesis, Naval
Postgraduate School, 1970.

Moore, D. G. , "Shear Strength and Related Properties of Sediments from

Experiment Mohole (Guadalupe Site)," Journal of Geophysical Research,
Vol. 69, No. 20, p. 4271-4291, 1964.

Richards, A. F., "Investigation of Deep-Sea Sediment Cores, Vol. I: Shear
Strength, Bearing Capacity, and Consolidation," Naval Hydrograohic
Office Technical Report No. 63, 1961.

Smith, R. J., "Engineering Properties of Ocean Floor Soils," Field Testing
of Soils, ASTM, STP No. 322, p. 559-566, 1963.

Smith, R. J., and Nunes, L. , "Undeformed Sectioning of Plastic Core
Tubing," Deep-Sea Research, Vol. II, p. 261-262, 1964.

140

Taylor, D. W., Fundamentals of Soil Mechanics, John Wiley and Sons,
New York, 1948.

Terzaghi, K. and Peck, R. , Soil Mechanics in Engineering Practice, p. 78-
100, John Wiley and Sons, New York, 1948.

Vey, E. , and Nelson, R. D., "Environmental Effects on Engineering

Properties of Deep Ocean Sediments," U. S. Naval Civil Engineering
Laboratory Report CR 67.020, 1966.

Vey, E., and Nelson, R. D. , "Environmental Effects on Engineering

Properties of Deep Ocean Sediments-Phase II," U. S. Naval Civil
Engineering laboratory Report CR 68.014, 1968.

141

INITIAL DISTRIBUTION LIST

No. Copies

1. Defense Documentation Center 2
Cameron Station

Alexandria, Virginia 22314

2. Library, Code 0212 2
Naval Postgraduate School

Monterey, California 93940

3. Oceanographer of the Navy 1
The Madison Building

732 North Washington Street
Alexandria, Virginia 22314

4. Professor R. J. Smith (Code 58Sj) 3
Department of Oceanography

Naval Postgraduate School
Monterey, California 93940

5. LCDR Richard K. Westfahl, USN 2
USS GEORGE C. MARSHALL (SSBN-654) (Blue Crew)

FPO New York 09501

6. Professor R. S. Andrews (Code 58Ad) 3
Department of Oceanography

Naval Postgraduate School
Monterey, California 93940

7 . Commander 10
Naval Facilities Engineering Command

Code 03

Washington, D. C. 20390

8. Department of Oceanography (Code 58) 3
Naval Postgraduate School

Monterey, California 93940

142

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DOCUMENT CONTROL DATA -R&D

(Security classification ol title, body ol abstract and indexing nnnot»tii,n mux! be entered when the overall repurt Is classified)

I originating ACTIVITY {Corporate author)

Naval Postgraduate School
Monterey, California 93940

la. REPORT SECURITY CLASSIFICATION

Unclassified

26. GROUP

3 REPORT TITLE

An Unconfined Compression Testing Machine for Marine Sediments

4 DESCRIPTIVE NOTES (Type ol report and.inc lus i ve dates)

Master's Thesis; September 1970

S au TMORISI (First name, middle initial, last name)

Richard Karl Westfahl

6 REPOR T D A TE

September 1970

7a. TOTAL NO. OF PAGES

141

76. NO. OF REFS

8a. CONTRACT OR GRANT NO

b. PROJEC T NO

»o. ORIGINATOR'S REPORT NUMBERISI

9fc. OTHER REPORT NOISI (Any other numbers that may be assigned
this report)

10 DISTRIBUTION STATEMENT

This document has been approved for public release and sale;
its distribution is unlimited.

II SUPPLEMENTARY NOTES

12. SPONSORING MILITARY ACTIVITY

Naval Postgraduate School
Monterey, California 93940

13. ABSTRACT

The two most common laboratory test methods used for measuring the un-
disturbed or original shear strength of marine sediments are the vane shear
test and the unconfined compression test. The application of the load in the
unconfined compression test is accomplished either in a strain-controlled or a
stress-controlled manner. An unconfined compression testing machine was con-
structed to allow application of the load by either the strain-controlled or
stress-controlled method, and it was specifically designed to accurately test
marine sediments having relatively low values of shear strength. A unique
feature of the apparatus is that it provides a continuous plot of displace- .
ment versus load throughout the test procedure. Tests for shear strength in
the two load application modes were conducted on gravity cores taken on the
continental slope between San Francisco and Monterey. Results of the tests
compared favorable with each other, as well as with values secured from vane
shear testing. The tests suggest that these particular sediments have friction
angles approximating 30 degrees.

FORM

I NOV 88

S/N 0101 -807-68t 1

1473

(PAGE 1 )

UNCLASSIFIED

143

Security Classification

A-31408

UNCLASSIFIED

Security Classification

KEY WO RDS

Compression Testing
Cores
Data

Deep Sea Cores
Deep Sea Sediments

Engineering Properties of Marine Sediments
Friction Angle
Marine Sediments
Sediment Engineering Properties
Sediment Cores
Sediments
Shear Strength
Unconfined Compression Test
Vane Shear Strength

DD/Nr6,1473 (back)

S/N 0101-807-6821

144

UNCLASSIFIED

Security Classification

A- 31 409

SHELF BINDER

S^S Syracuse, N. Y.
EST Stockton, Calif.

1 I APR 72

2 4 OCT 72

20U65
2 1 9 U 0

Thesis 123483

W482 Westfahl

c.l An unconfined com-
pression testing
machine for marine
sediments.

» » A»>R 72
^4UCT72

20M'»
2 1 8 U 0

Thesis 123483

W482 Westfahl

c.l An unconfined com-
pression testing
machine for marine
sediments.

'

3 2 '68 001 9